Various types of machine tools have spindles on which chucking elements can be located. The chucking elements, which may also be referred to as tool bit reception elements, are constructed to receive an end shank portion of the tool bit. They should be adaptable to various types of tool bits, while permitting quick release of the tool bits. Of course, they must retain the tool bits in an exactly centered position, so that the rotation of the tool bit will be true, with respect to the axis of rotating on the machine tool. It has been proposed to form the tool bits with a projecting retention stub; or, alternatively, to provide adaptor elements, arranged to be coupled to the tool bits, which then in turn will have this retention stub, and to so contruct the reception body that the retention stub is received therein and retained in position. The retention stub, typically, is located in a hollow space, surrounded by the side walls of the retention body. Clamping elements then are provided on the retention body to clamp the stub, and thereby hold the tool bit in position.
In a chucking system of this kind, known from German Patent Disclosure Document No. DE-OS 33 14 591, the retention bore, there called a reception bore, and the retention stub, acting as a centering pin, are conically embodied. The arrangement is such that the inside cone of the retention bore has a larger cone angle, by a predetermined small angular amount, than the outer cone of the retention stub, and by suitably embodying the retention stub and/or the receiving body, at least one of these two cones is elastically deformable until in the course of the longitudinal displacement of the conical gap between the two cones, the two cones rest against one another over a large surface area. In this chucking system, even if strong forces acting laterally upon the tool element are produced, a high degree of concentricity, or true rotation coaxial with the axis of rotation of the machine tool, is assured without making excessive demands in terms of manufacturing accuracy, and without difficulties in joining the tool element to the receiving body.
The chucking means that clamp the tool element to the receiving body comprise a coaxial clamping screw, which extending through a suitable longitudinal bore of the receiving body is axially supported on a shoulder of the receiving body and is screwed into an associated, coaxial threaded bore in the retention stub of the tool element.
This central clamping screw is accessible only from the backside of the receiving body, which under some circumstances is inconvenient, especially if the receiving body is inserted into a tool spindle by means of a chucking shaft. In a tool change, the receiving body must first be removed from the spindle, in order to make the clamping screw accessible, and to enable loosening the tool element that carries the tool. In practical terms, this means that a plurality of elements must be disassembled, beginning from behind. Even if the receiving body is formed directly by the hollow tool spindle, problems can arise in terms of how simple it is to actuate the central clamping screw with an automatic tool changing device.
The same is true, in principle, for fundamentally similar chucking systems, which have a cylindrical retention stub of the tool element, one of which is described by way of example in German Patent Disclosure Document No. DE-OS 32 37 128.
On the other hand, an actuation of the chucking means from the side of the receiving body permits a chucking system that is the point of departure for the present invention and is described in European Patent No. 0204 671 A2. In this chucking system, a coaxial chucking pin is screwed together with the cylindrical retention stub of the tool element, and on its portion located in the associated hollow space of the receiving body it has two opposed parallel plane surfaces, into which a set of teeth of sawtooth-like profile is cut. The chucking or locking elements, which are in the form of slides and are supported radially displaceably in corresponding guide bushings in the wall of the receiving body, are in turn correspondingly indented on the face ends oriented toward the chucking pin, and the arrangement is such that when the chucking elements are in the chucking position, at least two wedge-shaped faces, located axially succeeding the chucking pin teeth, mesh with corresponding oblique chucking faces spaced axially apart from one another, of the indentation of the chucking elements. The actuating means for adjusting the two diametrically opposed slides are provided by a clamping screw actuatable from the side of the receiving body by means of an Allen head tool, with the chucking screw extending through a corresponding through bore of the chucking pin in the vicinity of the teeth. This clamping screw can also be embodied as a turnbuckle screw or R/L screw, the right-hand and left-hand threaded portions of which are screwed into associated threaded bores of the slides.
Since the clamping screw crosses through the chucking pin, it must be removed entirely when the tool element is removed from the receiving body, that is, when there is to be a tool change; this is inconvenient and is also undesirable because there are loose parts involved; otherwise, the chucking pin must be slotted, which weakens it. Very stringent demands in terms of manufacturing precision must also be made, if it must be assured that with indentations meshing with one another, a plurality of teeth or tooth faces located axially spaced apart from one another must bear the same amount of weight. Even relatively slight inaccuracies in manufacture mean that the transmission of force takes place to locally limited portions of the surface area, which are then correspondingly overloaded. To avoid the situation in which either the teeth do not properly mesh with one another or the couplers that couple the tool element to the receiving body in a manner fixed against relative rotation will seize, the chucking pin must in practice therefore have a certain rotational mobility relative to the retention stub; this is attained, for example, by screwing the chucking pin onto the retention stub. In that case, first, a one-piece embodiment of the chucking pin on the retention stub, which would be desirable for some applications, would be impossible, while on the other hand even a slight rotation of the chucking pin with respect to the retention stub during the chucking operation, because of the threading, will lead to a not insignificant, undefined amount of axial motion of the chucking pin that also results in a non-uniform distribution of the tensile force to be transmitted to the axially successively located tooth faces of the teeth that come to mesh with one another.